The invention relates to superconductors in general and more particularly to a method and apparatus for the continuous, contactless testing of a long conductor consisting at least partially of superconductive material.
In the construction of superconducting coils such as magnet coils for generating strong magnetic fields or of superconducting windings for electric machines it is difficult to determine whether the conductor used, which as a rule is a conductor in wire, ribbon, cable or stranded form consisting of superconductive material and electrically normal-conducting metal, meets the specified requirements over its entire length, particularly with respect to its critical current and its magnetic field dependence as well as to other electrical and magnetic variables. Heretofore, sections were usually taken from the ends of the individual lengths of the conductor after manufacture. These were equipped with current leads and voltage probes and tested in an external magnetic field. However, it was still not known to what extent such test results were representative of the entire length of the conductor. Even if further samples are cut from the individual lengths of the conductor manufactured the values measured thereon will not necessarily be representative of the entire conductor length. Such a procedure furthermore has an undesirable consequence in that a length of conductor is cut up into smaller sections. Continuous testing for the respective conductor properties of interest over the entire length of the conductor and finding externally invisible faults, with, for instance, a lower critical current than the remaining conductor parts, have heretofore not been possible. On the other hand superconducting magnet coils particularly, often do not reach the operating performance data which are expected on the basis of measured values obtained from the end sections of the conductor or other samples. For this reason they have usually been relatively heavily overdesigned. Similar problems also arise with long superconducting wires and ribbons which are used in superconducting cables.